Gradiometer



Dec. 5, 1961 c. E. MILLER ETAL GRADIOMETER 2 Sheets-Sheet 1 Filed NOV.15, 1945 NTORS F, Jr.

W ATTORNEY Y 4 wrt 1 Coil INVE CHARLES E. MILLER WALTER H. BARKAS ROY E.-UPTEGRAF FIG.2

e 9 n lag Dec. 5., 1961 c. E. MILLER ETAL 3,012,191

GRADIOMETER Filed Nov. 15, 1945 2 Sheets-Sheet 2 INVENToRs CHARLES E.MILLER WALTER H. KAS

ROY E. UPT AFE-v ATTORNEY United States Patent Orifice 3,012,191GRADIOMETER Charles E. Miller, Walter H. Barkas, and Roy E. Uptegrati,ir., Seattle, Wash., assignors to the United States of America asrepresented by the Secretary of the Navy Fitted Nov. l5, 1945, Ser. No.628,912 l Claims. (Cl. 324-43) This invention relates generally toiniiuence-type detonating mechanisms for explosive ordnance, and moreparticularly to influence mechanisms of the gradiometer type, designedto automatically initiate rdetonation of the explosive charge uponproximity of extraneous magnetic material of predeterminedcharacteristics, corresponding to a target, yet so designed thatunwanted detonation will not occur due to the influence of the earthsmagnetic eld, or due to other factors to which it is desired that thedetonating means be unresponsive. Such devices are called gradiometersbecause they respond only to variations or gradients of the magneticfield that exist in the vicinity of magnetic materials, and are notaffected by a uniform magnetic iield.

It has of course been known for many years that a coil of wire attachedto a substantially rectilinearly moving item of ordnance such as aunderwater torpedo will have a voltage induced in it as the torpedomoves through the non-uniform magnetic eld present about a ship. 'Thisvoltage can be used to tire the-explosive charge of the torpedo as itcomes into the vicinity of a ship. As the torpedo, as during its runtoward the target, is always moving through the magnetic lield of theearth, however, any motion (roll, pitch or yaw) other thantranslational, will give voltages due to the changing components of theearths field through the coil. This is likely to result in prematuretiring of the torpedo, particularly if the behavior of the torpedo iserratic.

Theoretically the indicated difliculty can be overcome by substitutingfor the single coil a gradiometer consisting of two spaced-apart butidentical coils rigidly mounted with their axes parallel andelectrically connected in series opposition. It has been found, however,that such a system mounted in an arbitrary manner on a magnetic andelectrically conducting body, such as a torpedo, may also give a voltageoutput on motion in a uniform eld such as that of the earth, and sodefeat the purpose of use of the gradiometer principle. This voltagearises from the magnetism and eddy currents induced in the metalcomponents of the torpedo as it undergoes angular motion in the earthslield and which, in turn, give rise to time Varying magnetic gradientsand phase gradients in the region of the gradiometer.

One of the principal objects of the present invention, therefore, is toprovide an intluence operated exploder of the gradiometer typeparticularly. suitable for use in torpedoes and so designed as toproduce a voltage When moved through a non-uniform magnetic eld, as thelield about a ship, but to produce no response for any type of motion ina uniform eld (the eld of the earth), such as roll, pitch or yaw of thetorpedo during its run toward the target.

Another object of the invention resides `in the provision f l of anexploder mechanism of this character having simple and etfectiveadjustable means for compensating the coil system against any unbalancedconditions which would be produced by the presence of steel and/ orother magnetic parts of the torpedo such as the shell, the air flask andthe large magnetic iield gradients exist; i.e. to an area relativelyclose to the target.

Other objects of the invention will be evident from a consideration ofthis disclosure in its entirety.

In the drawings:

FIGURE l is a longitudinal sectional view of a gradiometer constructedin accordance with the present invention, certain parts being shown inelevation;

FIGURES 2 and 3 are longitudinal sectional viewsV on a larger scale ofopposite end portions of the gradiometer, particularly showing thecompensating means;

lFIGURES 4 and 5 are cross sectional views taken substantially on thelines 4 4 and 5-5, respectively, of FIGURE 3.

FIGURE 6 is a cross section taken substantially on the line 6-6 ofFIGURE 1;

FIGURE 7 is a cross section taken substantially on the line 7-7 ofFIGURE 2;

FIGURE 8 is a sectional perspective view showing the improvedgradiometer and related components installed in a torpedo war head; and

FIGURE 9 is a schematic wiring diagram.

The principal component of this invention is a gradienteter, from whichthe firing signal is derived, consisting of two identical coils, eachcontaining many turns of line copper wire. The two coils are spacedlymounted on a single core rod formed of a suitable magnetic alloy.A Thesingle rod mounting assures maintenanceV of the coils in accuratelyparallel relation. The whole gradiometer .assembly is so mounted in thetorpedo head as to give each coil, as nearly as possible, an identicalrelationship of symmetry or asymmetry with respect to the torpedo as awhole. This minimizes effects due to magnetic induction in the torpedo.The lack of fore and aft symmetry of the torpedo about the gradiometerassembly is compensated by a longitudinal corrector, while geometricaland magnetic asymmetries in an athwartship direction are compensated forbyan athwartship corrector, so oriented that no voltage is induced inthe coil system on changing the uniform component of magnetic field inan athwartship direction. Vertical asymmetries (along the axis of thegradiometer) are reduced by adjusting a vertical corrector screwprovided in one end of the magnetic rod and by the introduction ofphase-shift rings at each end of the gradiometer rod. Y y

Referring now in detail to the drawings, wherein like referencenumeralsV indicate like parts throughout the several views, the numerals1-and 2 designate, respectively, inner and outer concentric sleevesforming a double walled casing. The sleevesare preferably formed of non`in the hull within the sealed area surrounded by the secured ange rims.Through these openings end'caps 13,'

35 are accessible for purposes of adjustment as will pres-v ently morefully appear. Y

The outer casing sleeve 2 is threaded into, and sealed as by solder'withrespectv to, the -anges 3=and 4,' while the inner casing sleeve isrotatable;l Medially secured to and projecting forwardly of the casing 2is a corrector mounting element in the form Yofan internally threadedange 6 linto which alongitudinal corrector 7 comprising a cylindricalVmass off magnetic material'is designed to'bescrewed to clampanon-magnetic corrector ring 7"to secure phase balance, The sleeve 6 issecured to the casing as by silver solder in av longitudinal positionWhich Patented Dec. 5, 196i..

is determined by the magnetic characteristics of the individualinstallation in which the gradiometer is incorporated. lts function willpresently be discussed in detail.

The coils and 1.1 are substantially equidistantly spaced from themidpoint of the gradiometcr unit. The two coils are identical inconstruction, each being formed in two sections in the illustrativeembodiment shown, although this is of course a matter of choice, andeach complete dual coil assembly comprises a total of approximately100,000 turns of iine (number 40 B. & S. gauge) wire, layer wound on asuitable card-board or libre sleeve. The magnetic alloy core rod 12extends axially substantially the entire length of the inner casingsleeve l. At one end (FIG. 2) the core rod is keyed, as at 13 withrespect to the closure plug 1S. Plug 15 is formed of insulating materialsuch as plastic and screwed into the end of casing sleeve 1. A sealinggasket 16, of rubber, overlies the end of the casing and is held inplace by a sealing cap 17. Cap 18 is held in place by screws 19, asealing gasket 20 being contined beneath the cap for water-proofing.

A cable 21, which extends through a fitting 22 in the side wall of theflange 4, provides electrical connection between the coils 10 and 11 andthe ring apparatus, shown generally in FIG. 8 at 23.

The coils 10 and 11 are held in their spaced relation by central spacers24 and 25 of Bakelite or other insulating plastic. Mounted on the corerod 12 between said spacers is an athwartship corrector 2,6 of magneticmaterial such as cold rolled steel, contoured to dit the rod 12 and heldin place on the rod by Screws 27. A condenser 28, for -ltering outspurious impulses at high frequencies, such as might be caused byvibration of the torpedo, is mounted by a strap 29, the ends of whichare secured under the heads of said screws 27.

The end of the casing sleeve 1 which terminates in the flange 3 isclosed by an insulating plug 30 of Micarta or other suitable material,centrally bored to receive the end of the rod 12 which extendssubstantially therethrough. The end of the core rod is bored and tappedto receive a steel screw 31 which constitutes a vertical corrector andis designed to be locked in place by a nonmagnetic lock nut 32 or acement of litharge-glycerin or the like. A cap 32 is screwed into theplug 3) about the end of the corrector to protect the latter. A copperring 34 (or a series of rings) is carried about the rod 12 in a recessin the plug 30 and is held in place by the cap 33. The ring 34 acts as aphase shifter and provides an adjustment for synchronizing theelectromotive forces which are generated in the two coils of thegradiometer when the torpedo rotates in the earths magnetic iield. Thedimensions of the ring may be varied to effect the desired adjustment,and if it is desired a similar ring or rings may be employed at theopposite end of the assembly to extend the range of adjustment. Cap 35which closes the end of the flange 3 is held in place by screws 36.

To the end that the coils 10 and 11 will be properly positioned,magnetically, on the rod 12, shims, or spacers, 37, 37 are provided. Theshims 37 nearest the plug 15 may be made of copper to provide a phaseshifter cooperating with the ring 34, while the other shim-s are ofnon-conducting non-magnetic material.

The position of the inner casing sleeve 1 in the outer sleeve 2 isadjusted, to assure proper magnetic balance, by providing a seating ring38 and a clamping ring 39. As seen in FIGURE 3, a mounting flange ring49 is carried on the end of the casing sleeve 1 by means of the plug 30,which is threaded into ring 40 as well as into sleeve 1. Ring 40normally rests against the seating ring 38, and the position of ring 38will be seen to tix the longitudinal position of the core rod and coilassembly. Ring 38 is screwed into the threaded socket 41 of the endflange 3 the proper distance to locate the coils 10 and 11 for propermagnetic balance. When initial adjustments are being made, the propersetting for the ring 33 is ascertained by trial and the ring is thenlocked, as by tightening a set-screw 42 for setting the threads, beforethe gradiometer is set in position.

A pin 43 engages in a slot 44 to key the rod 12 against rotation and tohold the athwartship corrector against displacement from its properposition. By virtue of the key 13, the core rod, and so the corrector26, may be turned by turning the inner sleeve 1 when ring 313 is freedby releasing set-screw 42.

After the coils and corrector 26 have been properly located, the partsare locked in position by the ring 39 which, like the ring 38, ispartially -split radially and litted with a set screw for locking thethreads.

After the coils and the athwartship corrector have been properlypositioned in the casing 1, the interior of said casing is filled with asuitable potting compound (not shown).

The operation of the invention and the functions of the correctingdevices are believed to be obvious from the foregoing, but may brieflybe summarized as follows:

Although the coils 10 and 11 are made in two sections, each functions asa single coil and is shown as such in the schematic diagram, FIG. 9. Thetwo coil elements 10 and #11 are connected in series opposition, asthere shown, and their output is shunted by the condenser 23.

A magnetically permeable rod of `finite length such as the core rod 12,when subjected to translational and/or rotational motions in anon-uniform magnetic lield, will become so magnetically polarized thatthe magnetic inductions at any two points equdistant from the center ofthe rod at any given instant of time will not be equal. The corrector-sincorporated in the improved gradiometer equalize the magnetic lieldwhich surrounds the rod 12 as a result of movement of the torpedoassembly in the earths field. Thus, the system is initially in balance,and after the torpedo has been fired and reaches the non-uniformmagnetic iield of the target, electrornotive forces will be set up ineach of the coils 10 and 11. However, these forces will not be equalsince they have not been compensated by the correctors. An electromotiveforce accordingly results, and this is made to effect operation of the`tiring mechanism contained in the housing 23 (FIGURE 8). Suchmechanism, as previously stated, forms no part of the present invention,and may include suitable amplifying and primerdetonating means.

Each gradiometer is adjusted for the conditions obtaining in the torpedoin which it is installed. Longitudinal balance is effected by providinga steel corrector 7 (with corrector ring 7') of the proper length anddiameter which is positioned in the receptacle formed by flange 6 withits inner face the optimum distance from the wall of the casing sleeve2. Athwartship adjustment is accomplished by rotating the casing `1which rocks the rod 12 and with it the corrector 26.

Vertical adjustment is, of course, accomplished by setting the corrector(screw) 311 in its optimum position in the end of the rod 12, andadjusting the ring 34.

From the above description it will be understood that the inventionprovides a `grtnliometer type exploder of unitary, simple, rigid andwatertight construction, equipped with provision for balancing out alleffects which might give rise to premature firing as the torpedo movesthrough the magnetic tield of the earth on its 'way to the target. Whileit will be appreciated that the preferred form of the invention hereindisclosed 1s well calculated to fulfil-l the objects and advantagesprimarily stated, it will also be understood that the invention issubject to variation, modification and change within the spirit andscope of the subjoined claims.

What is claimed is:

1. A gradiometer for installation in a device having asymmetricmagneto-electric characteristics, comprising a core, a pair of coilshaving like characteristicsspacedly mounted on said core and connectedin series opposition,

whereby a signal may be derived from the output of said coils uponmovement of the gradiometer through a non-uniform field, and means forotsetting such asymmetric characteristics including a phase shiftingelement inductively coupled to one of said coils.

2. Means as set forth in claim 1 in which said phase shifting elementcomprises a substantially annular inductor mounted concentrically withrespect to said core and the last mentioned coil.

3. Means as set forth in claim 1 in which said core is substantiallystraight, said phase shifting element comprising a substantially annularinductor mounted concentrically upon said core near one end thereof, anda longitudinally adjustable supplemental core section adjacent said sameend of the core.

4. A gradiometer for installation in a device having asymmetricmagneto-electric characteristics, comprising a substantially straightcore, a pair of coils having like characteristics spacedly mounted onsaid core and connected in series opposition, whereby a signal may bederived from the output of said coils upon movement of the gradiometerthrough a non-uniform eld, said core being initially rotatablyadjustable about its longitudinal axis, means for olfsetting suchasymmetric characteristics, including an asymmetric mass of magneticmaterial mounted adjacent said core in the area between the coils andmovable by rotary adjustment of the core, and means for securing saidcore in it adjusted position.

5. Means as set forth in claim 4, in which said mass is carried by andinitially rotatably adjustable with said core.

6. A gradiometer adapted for installation in a device having asymmetricmagneto-electric characteristics, comprising a substantially straightcore, a pair of coils having like characteristics spacedly mounted onsaid core and connected in series opposition, whereby a signal may bederived from the output of said coils upon movement of the gradiometerthrough a non-uniform ield, said core being initially rotatablyadjustable about its longitudinal axis, and means for offsetting suchasymmetric characteristics, including an asymmetric mass of magneticmaterial mounted adjacent said core in the area between the coils andmovable by the rotary adjustment of the core, means for securing saidcore in its adjusted position, and a second asymmetric mass of magneticmaterial ixedly mounted in spaced relation to the first mentioned mass,said masses lying substantially in a plane perpendicular to the core.

7. A gradiometer assembly adapted to installation in a device havingasymmetric magneto-electric characteristics, comprising a substantiallystraight core, a pair of coils having like characteristics spacedlymounted on said core and connected in series opposition, whereby asignal may be derived from the output of said coils'V when the assemblyis moved through a non-uniform magnetic eld, an outer casing ofnon-magnetic material enclosing said assembly, an inner casingsurrounding said coils and core and rotatable within the rst mentionedcasing, said core being keyed to rotate with said inner casing, andmeans for offsetting such asymmetric characteristics, including anasymmetric mass of magnetic material secured to and rotatable with saidcore in the area between said coils.

8. LMeans as set forth in claim 6 in which said outer casing is fixed,and additional offsetting means comprising a second mass of magneticmaterial affixed to said outer casing.

9. A gradiometer for installation in a device having asymmetricmagneto-electric characteristics, comprising a core, a pair of coilshaving like characteristics spacedly mounted on said core and connectedin series opposition, whereby a signal may be derived from the output ofsaid coils upon movement of the gradiometer through a non-uniformmagnetic eld, and means inductively coupled to one of said coils, foroisetting such asymmetric characteristics. l

10. A gradiometer for installation in a device having asymmetricmagneto-electric characteristics, comprising a core, a pair of coilshaving like characteristics spacedly mounted on said'core and connectedin series opposition, whereby a signal may be derived from the output ofsaid coils upon movement of the gradiometer through a non-uniformmagnetic eld, and an auxiliary core adjustably secured to thefirst-named core `for correcting for lsaid asymmetric characteristics,said auxiliary core having a non-magnetic electrically conductive ringthereon to act as a phase correcting means.

` References Cited in the le of this patent UNITED STATES PATENTS

